The Boston Marathon bombing has intensified objections to the Gang of Eight’s so-called comprehensive-immigration-reform bill, and rightly so: The terrorist attack in Boston underlines several failures in our immigration system — failures that the bill under consideration would do little or nothing to rectify and would in some cases make considerably worse.

From a domestic-policy point of view, the most critical of these failures is the failure to maintain an immigration system oriented toward assimilation — the unapologetic expectation that immigrants will be fully immersed in American life. Assimilation has important cultural and economic benefits. It also makes immigrants less likely to become Islamist terrorists. The case of Tamerlan Tsarnaev — a non-citizen, charged in 2009 with a violent crime, flagged by a foreign intelligence service as a likely Islamic radical and terror threat, who traveled abroad to jihadist hot spots before returning to the United States to carry out his attack — suggests very strongly that our screening-and-evaluations system is broken. The case of Dzhokhar Tsarnaev suggests very strongly that our ability and willingness to fully assimilate immigrants is damaged, much as the London bombings pointed toward the United Kingdom’s inability or unwillingness to assimilate its immigrants.

Assimilation was never part of the agenda for the Tsarnaev family. The bombers’ parents claimed refugee status at a time when their place of residence was Kazakhstan, where there are many ethnic Chechens and little in the way of persecution that would justify refugee status. In fact, Tsarnaev père apparently had little reason to fear persecution in Russia, either: He returned there to live, and his son Tamerlan spent an extended period of time with him there, with side trips to the Islamist hot spot of Chechnya. Tamerlan never became a U.S. citizen (his flagging by the Russian intelligence service as a likely Islamic radical prevented that), his parents had returned to Russia, and he himself was in and out of the country a great deal: not exactly a candidate for what our forebears used to quaintly describe as our national melting pot.

The Gang of Eight bill would move us away from the traditional American ideal of assimilation rather than toward it. It would grant amnesty to many illegal immigrants with a tenuous connection to the United States, and to some who are not even currently living here. At the same time it would do a great deal to increase unskilled immigration, particularly by Hispanics. And it would create a new class of “temporary” workers and their families who would be expected to be in this country but not of it, until those standards are relaxed. Combine these features of the bill and what you have is not a recipe for welcoming new Americans but for encouraging cultural and linguistic separatism.

Most illegal immigrants come here for economic reasons, of course, and not out of any desire to join our country in any larger sense. Others cross the border illegally for entirely different reasons: Among those who took advantage of the 1986 amnesty was “agricultural worker” Mahmud Abouhalima, one of the terrorists who carried out the 1993 bombing of the World Trade Center. Terrorism aside, the main consequence of the 1986 amnesty was to encourage even more illegal immigration and, consequently, even less assimilation.

Rather than tighten refugee-status rules that the Tsarnaevs abused, the Gang of Eight bill would loosen them, for example by removing the one-year deadline for claiming refugee protection once on American soil and by abbreviating the review process for many such claims for protection.

Senator Lindsey Graham and other partisans of the Gang of Eight bill argue that its security provisions would help to ferret out threats. In practice, that is unlikely to be the case. Tamerlan Tsarnaev’s file should have had more red flags on it than a May Day parade, but that was not enough for the FBI to revisit his case or question his travel to Chechnya. As the 11 million illegals testify, our federal bureaucracy and law-enforcement agencies either cannot or will not enforce the immigration laws we already have on the books. The Gang of Eight bill would have them start enforcing our immigration laws — and administer a guest-worker program, and evaluate and process 11 million illegals, and improve the vetting of new immigrants. That is unlikely to prove successful. Senator Graham’s endless infomercial promises to the contrary are either cynical politics or sloppy thinking — both of which are in varying degree characteristic of the Gang of Eight’s overall approach. We would not be surprised if Senator Graham also promised that his bill would relieve lumbago and get rid of hard-to-clean grass stains.

Rather, there will be a great deal of political pressure to clear the “backlog” of legalization-seekers as quickly as possible. And though the possibility may not have occurred to Senator Graham, would-be terrorists are just as likely to take their chances staying illegal in a highly liberalized enforcement environment as to submit to federal background screening under the Gang of Eight bill.

While our piecemeal enforcement at the borders is a national scandal, those who enter the country legally but overstay their visas account for some 40 percent of illegals. The Gang of Eight bill would require the executive to establish a system of visa controls to address this problem. The problem is this: Congress passed a law requiring that very thing 17 years ago, and has on multiple occasions restated its demand that the law be enforced. So far, nothing doing. That pattern is characteristic of our immigration system in toto: a very fine collection of laws enforced in the most desultory fashion by a government beholden to business interests and ethnic lobbies hostile to the law as written. A government that was serious about restoring its credibility on the issue would at the very least get control of the border and fulfill Congress’s 17-year-old visa-control mandate without attaching a destructive amnesty to the package. Likewise, Janet Napolitano’s proposal for using improved passport technology to track those who come and go across our borders is a very fine idea on its own, no amnesty necessary. But the amnesty is the centerpiece here: To the bill’s proponents, everything else is an afterthought.

The Boston attack is far from irrelevant to the immigration debate. From the failures of law enforcement to the failures of assimilation, the case of the Tsarnaev brothers points both to what is wrong with our existing immigration system and what is wrong with the Gang of Eight’s plan to reform it.